1. Field of the Invention
The present invention relates to a water-in-oil type dispersed ink capable of use in a ball-point pen. More specifically, the invention relates to a water-in-oil type dispersed ink for use as a direct filling ink in a ball-point pen.
2. Description of Related Art
Since conventional water-based ball-point pens suffer drawbacks such as leakage, sagging, etc. of ink in spite of an excellent writing property as stated, for example, in JP-A-07-173,426, U.S. Pat. No. 4,671,691, EP 870,204, JP-B-64-8,673, JP-A-06-256,700, etc., these patent publications have disclosed techniques for improving such defective pens. For example, these documents describe techniques wherein the writing sensation and writing itself are similar to that found with conventional water-based ball-point pens such as imparting a shear thinning property to the ink, increasing the viscosity of the interior of the ink tank to a relatively high level, and/or utilizing the rotation of the ball to lower the viscosity of ink during the course of writing.
None of these techniques, however, sets the viscosity of the ink in the ink tank at a level that is high enough to sufficiently prevent the ink from leaking through or sagging down from the tip of the pen when the pen is exposed to a shock, nor do any of those techniques confer a perfect writing quality upon the pen. After all, since conventional techniques employ water as a main solvent and possesses other limitations affecting the supply of the ink to the tip of the pen and/or the permeation of the ink through the surface of the paper, the use of such water-based solvent's generally does not increase the viscosity of the ink as desired. Thus, the water-based ball-point pen ink generally sags down, offers only a limited resistance to a shock and produces a writing of insufficient fastness.
Further, since these techniques use water, they generally have a further technical problem; namely, since they generally include a water-soluble dye as a coloring material so as to improve the stability of the ink and to withstand the effect of aging, the fastness of writing quality is adversely affected. On the other hand, the use of a pigment improves the fastness of the writing while sacrificing of the ability of the ink to withstand the effect of aging.
In contrast, an oil-based ball-point pen manifests a sufficiently high ink-retaining property, but nevertheless generally does not permit smooth writing under a low writing pressure because the viscosity of the ink is typically very high. Thus with respect to oil-based inks, the density of the writing is generally insufficient owing to a poor supply of ink.
In recent years, JP-A-63-114,695, JP-A-06-31,314, and JP-A-07-196,972 have disclosed what is called "oil-based gel ink." None of these patents relating to gel inks incorporate water in their formulations. The oil gel inks described in these patents are disadvantageous since they fail to prevent the permeation of writing through the paper to the rear side when the viscosity of the oil gel ink is set at a low level, i.e., in the range of 300-3000 mPaS, which is a range that generally allows for ease in writing.